An inscribed gear type rotary pump such as a trochoid pump or the like is composed of an inner rotor having external teeth on an outer periphery thereof, an outer rotor having internal teeth on an inner periphery thereof, a casing that has a central plate and side plates for accommodating the inner rotor and the outer rotor, and the like.
The outer rotor and the inner rotor are disposed in the casing in a condition where the external teeth and the internal teeth are meshed to each other, and a plurality of gaps is formed by these meshed teeth.
It is necessary to seal low-pressure parts and high-pressure parts in such a rotary pump.
Therefore, one end surface of the rotary pump in an axial direction is sealed by pressing sealing members that are provided in the side plates to the rotors, and another end surface is mechanical sealed by pressing the rotors directly to the side plates.
Further, a recess is formed in the central plate and a sealing member is disposed in the recess, and an outer periphery of the outer rotor is sealed by bringing the sealing member into contact with the outer periphery of the outer rotor.
However, since the rotary pump configured in this manner has adopted a mechanical seal, torque loss of the rotary increases in slid-contacting surfaces between the side plates and the rotors, hence heat is generated accompanying the slid-contacting and a heated portion expands so that there is a possibility to reduce a pump discharge capacity.
Therefore, a rotary pump that has a structure to reduce the slid-contacting area between an end surface of the outer rotor in an axial diction and an end surface of the plate by forming an oil groove in a position in the side plate where a center line of the rotors and an outer edge of the outer rotor intersects is proposed in Japanese Patent Application Laid-Open Publication No. 2007-263116.
By reducing the sliding contact area between the end surface of the outer rotor in the axial diction and the end surface of the plate, it is possible to reduce the torque loss.
Since the contacting area between the end surface of the outer rotor in the axial diction and the end surface of the plate can be reduced corresponding to an area of the oil groove in the rotary pump disclosed in the Publication No. '116 mentioned above, contact resistance between the side plates and the outer rotor can be reduced.
However, since the contacting area, between the outer rotor and the side plates is reduced, load applied to contacting portions is increased correspondingly; an amount of wear of the outer rotor and the side plates increases.
Further, since the oil groove is formed so as to reach a gap formed between the central plate and the outer periphery of the outer rotor in an extensive range along the outer edge of the outer rotor in the rotary pump disclosed in the Publication No. '116, the reduction of the contacting area becomes large and the amount of wear becomes increased.